1. Field of the Invention
The present invention relates to an optocoupler having a light-emitting semiconductor component and having a light-receiving semiconductor component that are connected to one another via an electrically-insulating, light-transmissive coupling agent.
2. Description of the Prior Art
Optocouplers of the type set forth above are generally known in the art. They serve the purpose of reaction-free signal transmission between two voltaically-separated circuits, namely a primary circuit and a secondary circuit. At the primary side, they are composed of a light-emitting semiconductor component, for example a light-emitting semiconductor diode (LED), and, at the secondary side, they are composed of a light-receiving semiconductor component, for example a photodiode or a phototransistor. These components are optically coupled to one another. For example, a transparent plastic is used as a coupling agent.
The optocouplers that are currently in most wide-spread use have a bipolar transistor at their secondary sides. The output of the coupler therefore represents a variable resistor having a transistor characteristic.
An optocoupler that outputs a voltage on the order of magnitude of 5 volts at the secondary side is required for the drive of field-effect transistors, particularly metal-oxide-semiconductor (MOS) transistors, in particular without an additional voltage source. Such a coupler is particularly multiply required for a test access per telephone subscriber line in a computer-controlled telephone switching system.
Optocouplers of this type having a voltage output require the series connection of a plurality of photoelements, i.e. active two-terminal networks having a pn junction that have a relatively low internal resistance. They can be discretely constructed or can be constructed with a hybrid technique that combines a plurality of chips. When one wishes to monolithically integrate the photoelements, then the individual photoelements must be separated from one another by dielectric insulation. Photoelements in amorphous or crystalline semiconductor layers on insulators, for example, amorphous silicon or silicon dioxide layers are likewise useable. Due to the complex structure, however, all of these possibilities are complicated and involve a time expense or, respectively, cost expense in manufacture.